Oral sealing using glue: a new method to distinguish between intestinal and dermal uptake of metals in earthworms

Abstract

Earthworms may take up chemicals from soil and pore water, both through their skin (dermal) and by ingestion (oral). It remains unclear, however, what the relative importance of these pathways is. To assess bioavailability of pollutants in soil to earthworms, it is necessary that the contribution of each pathway is known. Lumbricus rubellus were sealed by means of medical histoacryl glue, to block ingestion of soil particles and pore water. For 6 d, these earthworms showed good survival and vitality and no soil ingestion was found. Equal metal uptake was found by sealed and unsealed earthworms exposed to an inert sand matrix continuously flushed with contaminated water. Therefore, pore water uptake via ingestion contributes little to metal accumulation. Uptake rates of Cd, Cu and Pb in sealed and unsealed earthworms exposed to two contaminated field soils were similar. Uptake and elimination kinetics of Zn were significantly lower in sealed earthworms exposed to one of the two field soils. Body concentrations of Cu and Pb could be completely attributed to the dermal route. For internal Cd and Zn concentrations, however, 0–17 and 21–30%, respectively, were derived from ingestion. It is concluded that for metals the dermal route is the uptake route of importance. The sealing method described here may be useful in a variety of earthworm nutrition and contamination-effect studies.